This invention relates generally to injection molding cooled gate and cavity inserts and more particularly to such an insert with rib portions projecting into the cooling fluid chamber to improve the combination of cooling of the melt and structural strength of the insert.
Inserts which define a portion of the cavity and through which the gate extends to convey melt from a heated nozzle to the cavity are well known. Such inserts having a circular chamber for cooling fluid flowing around the gate are also known. U.S. Pat. No. 4,622,001 to Bright et al. which issued Nov. 11, 1986 shows a two-piece insert with a cooling chamber which is prone to leakage. U.S. Pat. No. 4,687,613 to Tsutsumi which issued Aug. 18, 1987 apparently illustrates a one-piece insert with a circular cooling chamber, but no way of making it is described. The applicants' Canadian Patent Number 1,314,370 which issued Mar. 16, 1993 shows a one-piece gate and cavity insert with a circular cooling chamber and also describes how to make it.
In most injection molding applications, the cost effectiveness of multi-cavity molding has made compact size a very important factor. While rapid cooling of the melt is important to reduce cycle time, higher injection pressures in the cavity have also made structural strength of the mold an increasingly important consideration. This is particularly true for molding polyethylene terephthalite (PET) preforms for beverage bottles which require large multi-cavity systems with short cycle times to be competitive. Of course, cooled gate and cavity inserts have the problem that increasing the size of the cooling fluid chamber to provide more cooling results in a loss of structural strength to withstand the injection and sealing pressure in the cavity. Furthermore, the thicker the cavity wall around the gate, the more insulation it provides and thus the more cooling that must be provided by the cooling fluid. Thus, all of the previous gate and cavity inserts have the disadvantage that the combination of melt cooling and structural strength they provide is insufficient for some applications such as molding PET bottle preforms.